Why is the volume lower than is was previously when it was essentially the same as music playback?
When you are mixing information from multiple channels, you have to reduce the volume to prevent clipping.
If you mix a stereo signal down to mono for example, you need to reduce the volume on each channel by 6dB.
If you did not do that, if both channels play anything louder than -6dB at the same time, the result would sum up to be
above 0dB which would be clipped. (distorted)
If you mix a 5.1 signal down to stereo, you now have six channels of information being mixed into two, so you need to reduce the volume even further to prevent clipping.
A fully normalized downmix should use:
Left: -12.1 dB
Right: -12.1 dB
Center: -15.1 dB (3dB lower than L/R because it is being sent to both)
Sub: -8.0 dB (4dB louder than L/R because LFE is normally +10dB and summing bass frequencies among two channels is perceived as +6dB)
Left Surround: -15.1 dB
Right Surround: -15.1 dB
With this downmix, if all channels have an 0dB signal played at the same time, the total in the stereo downmix would be exactly 0 dB.
If any of the channels were louder than this, the signal would be driven above 0 dB and clip.
With 7.1 you have to reduce the volume even further:
Left: -13.5 dB
Right: -13.5 dB
Center: -16.5 dB
Sub: -9.4 dB
Left Surround: -16.5 dB
Right Surround: -16.5 dB
Left Rear: -16.5 dB
Right Rear: -16.5 dB
With build 124, what Media Center is
supposed to do, is use the peak values from analyzed audio to avoid reducing the volume as much.
If the loudest channel is -6dB, then the values for everything in the mix could be pushed up by as much as 6dB without clipping.
If one channel is -6dB and the others are even lower than that, you would be able to push up the volume of the downmix even further than 6dB while still avoiding clipping.
However, the downmix currently used does not appear to be correct (too much LFE) and the compensation for peak levels does not seem to work correctly in this build. (clipping protection is being enabled)
Something I would also like to see, is the option to normalize everything relative to the volume of a 7.1 signal. (reduce stereo playback by 13.5dB, and 5.1 playback by 1.4 dB)
It would reduce the volume of all video playback, but mean that volume is consistent regardless of the source format.
Something like that could theoretically be done with zones and zone switch, but what a pain that would be.